In two studies published in the April issue of Anesthesiology, anesthesiologists from the Duke University School of Medicine report new findings that may help to identify patients at greater risk of experiencing postoperative delirium.

Postoperative delirium is a state of confusion affecting approximately 15 percent of older surgical patients.

Episodes of delirium may occur for several hours or even for days. Some patients may even experience a longer-lasting state of confusion with a serious decline in cognition and attention. Postoperative delirium has been associated with increased postoperative complications, medical costs and death.

The first study, from Terri G. Monk, M.D. and colleagues, was originally presented as an abstract at the 2008 American Society of Anesthesiologists Annual Meeting, and explored the impact of multiple risk factors on the probability for postoperative delirium among older adults undergoing non-cardiac surgery with general anesthesia.

100 patients 50 years or older undergoing non-cardiac surgery were submitted to a preoperative screening for depression and a battery of five tests designed to measure general cognition and their ability to process information, concentrate and self monitor. Postoperative delirium occurred in 16 percent of patients. Results indicated that the most reliable predictors of postoperative delirium were tests measuring depression and cognitive flexibility. Patients whose scores indicated underlying depression and less cognitive flexibility, also known as executive function, were most likely to experience delirium following their surgery.

“This study demonstrates that a short preoperative test lasting just 10 minutes or less can help to identify which patients may be at risk for the development of postoperative delirium,” said Dr. Monk. “Once patients at risk can be identified, interventions to prevent or minimize delirium can be investigated and implemented, to the benefit of the aging population.”

A companion study in the April Anesthesiology evaluates the relationship between executive function, depression and delirium, furthering evidence that patients who exhibit test results of executive dysfunction and depression before surgery are most at risk for developing postoperative delirium.

Patrick J. Smith, M.A., and colleagues (including Dr. Monk) at Duke, performed a retrospective review of 998 patients undergoing major non-cardiac surgery. Patients were screened preoperatively using tests to measure confusion, executive function and depression. 3.5 percent, or 35 patients, developed delirium following surgery. Further analysis of preoperative test results and the development of delirium revealed that tests of executive tasks with greater complexity such as the Stroop Color Word Interference Test, are more strongly associated with postoperative delirium than simpler tests of executive function or tests of general cognition. Patients who exhibited both executive dysfunction and clinically significant depression were determined to be at greatest risk for developing delirium postoperatively.

Dr. Monk added, “Recent studies estimate the national burden of delirium of the health care system may be as high as $152 billion each year. These results are an important first step in developing practical and predictable screening tools to identify patients at risk and develop preoperative interventions to reduce the incidence of delirium and reduce associated health care costs.”